1. Field of the Invention
This invention relates to a method and apparatus for detecting and locating current leakage paths along the length of an electrically conducting elongate member, in particular pipes or cables. This invention also relates to a method for detecting oscillatory motion of such an elongate member under water.
2. Description of the Related Art
The type of pipe or cable to which the method of the present invention can be applied is one which is electrically conducting along its length and in its ideal state is electrically insulated from its surroundings. However, in the event of corrosion along the length of such pipes, electric current leakage paths are formed between the pipe and its surroundings. In order to detect corrosion, or other forms of damage which result in the formation of leakage paths along the length of a pipe, a typical method involves connecting a section of the pipe to a Wheatstone bridge type arrangement thereby enabling its resistance to be measured and using this resistance to determine whether there are any leakage paths formed between the pipe and its surroundings. However, this has the disadvantage that whilst an electric current leakage path can be detected, the location of that leakage path can be difficult to determine. In addition, this method requires that the pipe is probed extensively along its length and this can be time consuming and when the pipe is underground or under water, very expensive. Another method of detecting corrosion is to merely visually inspect the pipes which again is very expensive.
DE-A-3727224 discloses a measuring system for locating leakage faults on cables in which a pair of parallel conductors sheathed in an insulating material are connected into a bridge circuit and the location of a fault in the insulating material that leads to a leakage is determined by balancing the bridge circuit.